The introduction of new wireless radio access technologies usually occurs in stages due to financial and logistical considerations. For example, it is common for evolved radio access technology (RAT) infrastructure to be implemented initially in areas with higher population density amidst existing radio access technology infrastructure. Such implementations often require multi-mode user terminals supporting the different radio access technologies. The emerging 3GPP LTE radio access technology will be likely be implemented using multimode user equipment (UE) that supports OFDM and CDMA technologies operating simultaneously in neighboring frequency bands. In the United States, for example, simultaneous activation (i.e., uplink transmission) of a CDMA RAT operating at 850 MHz and an OFDM RAT operating at 700 MHz may result in desense of one or the other radio access technologies.
Emerging broadband wireless networks such as 3GPP LTE must solve the problems of minimizing the power amplifier (PA) power consumption (or peak and/or mean current drain), cost and the complexity required to deliver a specified conducted power level in the context of new modes of system operation. For example, PA performance must be optimized in the presence of numerous different frequency or spatially adjacent radio access technologies, including GSM, UMTS, WCDMA, unlicensed transmitter and receivers, among other radio access technologies.
Exemplary cellular communication networks include 2.5 Generation 3GPP GSM networks, 3rd Generation 3GPP WCDMA networks, and 3GPP2 CDMA communication networks, among other existing and future generation cellular communication networks. Future generation networks include the developing Universal Mobile Telecommunications System (UMTS) networks, Evolved Universal Terrestrial Radio Access (E-UTRA) networks. The network may also be of a type that implements frequency-domain oriented multi-carrier transmission techniques, such as Frequency Division Multiple Access (OFDM), DFT-Spread-OFDM (DFT-SOFDM), Interleaved Frequency Division Multiple Access (IFDMA), etc., which are of interest for future systems. Single-carrier based approaches with orthogonal frequency division (SC-FDMA), particularly IFDMA and its frequency-domain related variant known as DFT-SOFDM, are attractive in that they optimize performance when assessed using contemporary waveform quality metrics, which may include peak-to-average power ratio (PAPR) or the so-called cubic metric (CM).
In OFDM networks, both Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM) are employed to map channel-coded, interleaved and data-modulated information onto OFDM time/frequency symbols. The OFDM symbols can be organized into a number of resource blocks consisting of M consecutive sub-carriers for a number N consecutive OFDM symbols where each symbol may also include a guard interval or cyclic prefix (CP). An OFDM air interface is typically designed to support carriers of different bandwidths, e.g., 5 MHz, 10 MHz, etc. The resource block size in the frequency dimension and the number of available resource blocks are generally dependent on the bandwidth of the system.
User equipment operating in a cellular network operate in a number of ‘call states’ or ‘protocol states’ generally conditioned on actions applicable in each state. For example, in a mode typically referred to as an ‘idle’ mode, a UE may roam throughout a network without necessarily initiating or soliciting uplink or downlink traffic, except, e.g., to periodically perform a location update to permit efficient network paging. In another such protocol state, the UE may be capable of initiating network access via a specified shared channel, such as a random access channel (RACH). A UE's ability or need to access physical layer resources may be conditioned on the protocol state. In some networks, for example, the UE may be permitted access to a shared control channel only under certain protocol-related conditions, e.g., during initial network entry. Alternatively, a UE may have a requirement to communicate time-critical traffic, such as a handover request or acknowledgement message, with higher reliability.
The various aspects, features and advantages of the invention will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.